Literature absorption coefficients dispersion curves for PSi, Si and eumelanin. Comparison of the absorption coefficients dispersion curves reported in literature for several materials: eumelanin film, thin (80 nm, full squares), and thick (800 nm, empty squares), ; 58 % porosity p-type (inverted triangles) and 78 % p+-type (upright triangles) porous Si, ; and bulk Si (full circles) . The plot shows how the absorption coefficient of eumelanin is significantly larger than that of PSi, becoming more than one order of magnitude larger for wavelengths longer than about 650 nm. It is worth noting that this is also valid with respect to the undoped bulk Si.
Mula et al. Nanoscale Research Letters 2012 7:377 doi:10.1186/1556-276X-7-377